1. Field of the Invention
The present invention relates to the shaping of partially completed books and particularly to rounding the spines of book blocks. More specifically, this invention is directed to spine-rounding apparatus which acts from the opposite sides of a book block to controllably apply pressure thereto and especially to the exercise of control over book block spine rounding elements so as to cause such elements to execute rolling movements on the sides of a book block. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
The spine-rounding of book blocks is an operation performed in the course of book manufacture. The spine-rounding operation causes the book block spine to assume the desired shape for subsequent binding while, at the same time, a complementary shape is imparted to the cut fore edge of the block. The conventional technique for spine-rounding implements what is known in the trade as the roller-rounding principle.
During roller-rounding, the individual leaves or printed sheets which comprise the book block are smoothly and progressively displaced relative to one another as a result of the simultaneous rolling movement of grooved rounding rollers on the book block opposite sides. This rolling movement is caused to progress through a defined rotation angle concurrently with the application of pressure so that, as the book block passes through the rounding rollers, the leaves or printed sheets are pushed progressively further forward in the direction of the block center. The rounding operation should result in the book block spine being configured as an arc of a circle or a somewhat flattened arc. This shaping is critically important in order to provide the desired book block spine profile and to permit the performance of the subsequent book block backing or binding operation. Restated, in the course of manufacture of a book, the spine of a book block must be formed into a rounded shape with the degree of rounding being determined by a rounding coefficient which is a function of the spine arc and the book block thickness. When the roller-rounding principle is applied, the spine shape is primarily influenced by the pressure exerted by the rounding rollers, the angle through which the rollers rotate and the diameter of the rounding rollers. The spine shape is also influenced, to a lesser degree, by other factors.
In prior art book block shaping machines which implement the roller-rounding principle, a rounding roller with a single diameter is employed for all sizes of book block. Accordingly, bearing in mind the above-listed principle factors which influence a roller-rounding process, it is inevitable that a single diameter roller will be able to satisfy the manufacturing requirements to only a limited extent. Restated, the desired spine rounding, in the shape of an arc of a circle, can be achieved only when the roller diameter and the book block thickness are matched to one another. When small format book blocks are shaped, the gross mismatch between the rounding roller diameter and the book block thickness produces the condition where an effective rounding stroke, as required for the desired rounding result, cannot be achieved. Conversely, when large-format book blocks are to be shaped, the relatively small-diameter rounding roller is incapable of exerting the requisite pressure forces on the central portion of the book block to produce the requisite leaf displacement.